SOD1 and schizophrenia: It was demonstrated that (a) there was no significant correlation between transferrin gene polymorphism and the susceptibility to schizophrenia; (b) rs3811655-G variant was associated with more severe symptoms, worse cognition, and higher SOD activity in schizophrenia; (c) mediation analyses indicated that psychotic symptoms played a fully intermediary role between either Cu/Zn-SOD or Mn-SOD activity and cognition; (d) the mediating role of psychotic symptoms on the relations between Cu/Zn-SOD and cognition may vary with the transferrin gene polymorphism (rs3811655).